The invention relates to a control device for the control of a hydraulic consumer having a hydraulically actuable directional valve in accordance with the description herein. The invention furthermore relates to a hydraulic pilot control device in accordance with the description herein.
Hydraulic control devices having hydraulically actuable directional valves are used inter alia in hydraulic systems of vehicles. A plurality of directional values are expediently interlinked in the form of valve disks in a so-called control block. Using such a hydraulic control device, lifting devices of a lift truck or of an agricultural tractor, loading cranes, the bucket of a wheeled loader or also driving and steering functions of a vehicle are operated hydraulically; in the event of a control regulated by flow requirement (load sensing), individual valve disks have a pressure balance for the control of the hydraulic pressurizing medium flow flowing across the valve.
Mineral oil is usually used as the hydraulic pressure fluid or pressurized medium in industrial hydraulics and mobile hydraulics. However, a water-based pressurized medium is also used for certain areas of application. The term fluid will be used in the following for hydraulic fluids.
A hydraulic control device is known, for example, from DE 197 15 020 A1 Directional valves are arranged in different valve disks for the control of hydraulic consumers. The directional valves have valve pistons for the control of pressurized medium connections and in each case two spring chambers. A control pressure is built up in a spring chamber to actuate the valve piston against the spring bias. The respective control pressure is generated by an electrically actuated pressure control valve. Two respective pressure control valves are provided as pilot control valves for a valve disk. The valve piston can thus be deflected in two mutually oppositely set directions. The electric control of the pressure control valves as a rule takes place by means of an operating element.
In rare cases, electrically controlled pressure control valves fail in that the control piston of the pressure control valve jams and can no longer be electrically actuated. One reason for this can be dirt particles carried along in the fluid flow. If the control piston is just located in the control position at which the output of the pressure control valve is blocked against the control fluid supply port and the tank port, no more control fluid can be displaced out of the corresponding spring chamber of the directional valve. The directional valve is thus blocked in the controlled position and the movement carried out by the hydraulic consumer cannot be stopped. Such a block can also not be released by a counter-control (counteraction) at the operating element whereby the oppositely disposed spring chamber is subjected to control pressure via the corresponding control pressure valve since, as said, not fluid can be displaced from the blocked spring chamber.
DE 103 08 910 A1 deals with a safety valve which is integrated into the supply line of pilot control valves. The described, electromagnetically actuated 3/2 way valve can connect the supply line of the pilot control valves either to a pressurized medium source or to a container. A relief passage from the output port to the spring chamber is provided in the valve disk of the 3/2 way valve. When the magnet is actuated, the relief passage is blocked by the magnetic plunger. When the magnet is not actuated, the relief passage to the spring chamber, and thus to the container, is open, provided that the valve disk does not follow the magnetic plunger. The complex and/or expensive construction is disadvantageous in this valve. Nor can the construction be transmitted easily to pilot control valves formed as pressure reducing valves. In addition, the supply line cannot be relieved if a continuous actuation occurs due to an error in the control electronics of the 3/2 way valve.